1. Field of the Invention
The present invention relates to coordinate input apparatuses that optically detect a coordinate location input on a coordinate input surface using a pointer, such as a finger, for inputting and selecting information. The present invention particularly relates to removable and portable coordinate input apparatuses.
2. Description of the Related Art
Thus far, various types of coordinate input apparatuses (such as touch panels, digitizers, and so on) have been proposed or commercialized as this type of coordinate input apparatus. For example, touch panels and the like, which allow a PC (personal computer) or the like to be operated with ease simply by touching a screen with a finger without using a special tool, have become widespread.
Various systems are used in such coordinate input apparatuses, such as panels that employ resistive films, panels that employ ultrasound waves, and so on. As a system that employs light, a retroreflecting member is provided on the outside of the coordinate input surface, light from a light-emitting unit is reflected by the retroreflecting member, and the distribution of that light amount is detected by a light-receiving unit, thereby detecting the direction of a light-shielding region in which the light has been shielded by a pointer such as a finger (a light-shielding object) within the coordinate input region. This optical light-shielding coordinate input apparatus, as it is known, then determines a light-shielding position, or in other words, the coordinates of a coordinate input position (see, for example, U.S. Pat. No. 4,507,557).
The configuration illustrated in FIG. 14 indicates a generalized example of the configuration disclosed in U.S. Pat. No. 4,507,557. FIG. 14 illustrates sensor units 901 arranged on both ends of a coordinate input surface, a coordinate input surface 902 used when inputting coordinates, and a retroreflecting member 903 that surrounds the coordinate input surface 902 on three sides and retroreflects light that has entered back in the direction in which the light entered.
The sensor units 901 include light-emitting units and light-receiving units (not shown). The light-emitting units irradiate light that expands in a fan shape almost parallel to the coordinate input surface 902, whereas the light-receiving units receive the light that returns recursively having been reflected by the retroreflecting member 903. The coordinate input apparatus is capable of calculating a position 904 of coordinates input into the coordinate input surface 902 based on shielding angles θL and θR of the respective light detected by the two sensor units 901 and the distance between the sensor units 901.
In such optical light-shielding coordinate input apparatuses, it is necessary, in order to calculate a precise coordinate input position, to arrange the sensor units 901, which include the light-receiving units, at predetermined positions. However, there is a limit, in terms of precision, as to how accurately the sensor units 901 can actually be arranged, and it is also thought that the positions may shift after attachment as well. A technique for carrying out what is known as calibration, or reference point setting in which inputs are carried out at a plurality of pre-set locations in the coordinate input region, has been disclosed as a method for correcting positional shift in the sensor units 901, as in, for example, Japanese Patent Laid-Open No. 2007-265417.
Meanwhile, Japanese Patent No. 3964079 discloses a technique in which sensor units are once arranged at pre-set positions and the light emitted from one of the sensor units is received by the other sensor unit, and shift in the sensor unit that receives the light is detected based thereupon.
However, in the aforementioned conventional related art, the method that carries out reference point setting requires additional operations in forcing a user to point of a plurality of points, and is thus problematic in terms of operability. Furthermore, the technique disclosed in Japanese Patent No. 3964079 is capable only of detecting shifts in the case where the two sensor units are first arranged in pre-set positions. In other words, the positions of the sensor units cannot be found in the case where a user has arranged those sensor units in any desired positions.
Meanwhile, coordinate input apparatuses can also be considered for use in office and educational settings, being used at destinations as large-screen electronic dry-erase boards themselves, or by being attached to existing blackboards or dry-erase boards, large-screen displays, and so on, in order to input coordinates. In other words, a user packs up and only transports a sensor unit portion and the units that belong thereto, and attaches the sensor units and the like to the flat plane for a predetermined usage region. Such a configuration is not only portable, but is also easy to attach and remove. However, in such a case, it is difficult for the user to arrange of the sensor units accurately, at a certain level of precision, around the coordinate input region. In other words, this configuration has a unique problem, which does not occur in a conventional type of apparatus in which the sensor units are arranged in a fixed manner in predetermined positions.
It is necessary, in a removable, portable, and compact coordinate input apparatus, to first obtain the coordinate information of the positions of the sensor units attached by the user at the desired positions.
The technique disclosed in Japanese Patent No. 3964079 assumes that the sensors are first arranged at known/prescribed distances and positions, and then detects differences from the initial state as correction amounts. Accordingly, the configuration cannot calculate positions and directional orientations in the case where the sensor units have been arranged in arbitrary positions. Meanwhile, with the technique disclosed in Japanese Patent Laid-Open No. 2007-265417, constituent elements, such as reference marks for the input region, are necessary in portions aside from the sensor units, which makes it necessary for the user to perform further additional operations.